Loud Whining Noise from Inside the Engine near the Alternator Area


Asked by Nov 02, 2015 at 02:15 PM about the 2004 Toyota 4Runner SR5 4WD

Question type: Maintenance & Repair

The whining noise started 6 months ago and is getting louder.  Took it to a
mechanic who listened with a long screw driver and said it's from the
alternator bearing.  He replaced it, but the noise still there.  The noise
seems to come from inside the engine above the alternator. The noise gets
louder as the engine is rev'ed up.  What could cause such a noise inside
the engine?  Please help.  Thanks.

5 Answers


the alternator drive belt will have tensioners in it, it is the bearings in the tensioners that have gone, the technician should have noticed this on basic inspection, to replace the tensioners is a job you can do yourself and change the belt whilst you are under the hood.


if it is the tensioners and belt that are worn, chances are the cambelt may need changing (if fitted) a failing cambelt will result in serious damage and you may need a rebuilt motor.

Bob Beaman

If it were mine.....I would remove the serpentine belt and briefly start the engine to see if the noise is gone (do not run the engine for more than 30 seconds with the belt removed or it may overheat). If the noise remains probably the timing belt tensioner, idler or related part. If the noise disappears when the serpentine belt is removed, one of the accessories the belt drives likely has a bad bearing or other issue.


Bob, thank you very much for your reply. Very intelligent way of diagnosing the problem. I will pass on your advise to my mechanic. One more question: my 4Runner 4.0 engine has a timing chain, not timing belt. Is the timing chain set up the same way as a timing belt? With tensioner, idler and related parts? Thanks a lot.

1 out of 1 people think this is helpful.
Bob Beaman

Yes timing chains have rubbing blocks, and hydraulic tensioners. No point in getting worried about a timing chain unless it starts to make noises on start up. Good quality engine oil at the recommended grade, changed at the recommended interval and a quality oil filter will help maximize the life of the timing chain and the rest of the engine.

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